The Turtle Bluff Member (TBM) of the Bridger Formation in southwestern Wyoming, formerly known as the Bridge E, is designated as the stratotype section for the earliest Uintan or biochron Ui1a of the Uintan North American Land Mammal age. The TBM overlies the Twin Buttes Member of the Bridger Formation, upon which the Twinbuttean Subage or biochron Br3 of the Bridgerian North American Land Mammal age is based. For over a century, the TBM yielded only a few fragmentary specimens, but extensive field work over the last 23 years has resulted in the discovery of numerous mammal fossils from the member, which provides an unprecedented opportunity to better define this poorly known interval. This is the second in a series of three papers that provides detailed descriptions and taxonomic revisions of the fauna from the TBM. Here we document the occurrence of 21 mammal species from the TBM: two species of the primitive insectivore-like mammal Apatemys; 11 species of 'insectivores' including two new species, Nyctitherium gunnelli and Entomolestes westgatei; the primitive carnivoran Viverravus gracilis; the small ungulate-like (condylarth) mammal Hyopsodus lepidus; the giant primitive ungulate Uintatherium anceps; the early brontothere (rhino-like) Wickia; the small rhino Triplopus; the small horse Epihippus; and two artiodactyls (the primitive Homacodon and a new species, Merycobunodon? walshi). A greater understanding of the faunal composition of the TBM allows a better characterization of the beginning of the Uintan and further clarifies the Bridgerian-Uintan transition.

Paul Murphey received a doctorate in geological sciences with an emphasis in vertebrate paleontology from the University of Colorado at Boulder in 2001. His professional experience includes appointments as the Collections Manager of Paleontology, Geology and Osteology in the Geology Section of the University of Colorado Museum; instructor in the Museum and Field Studies Program at the University of Colorado Museum; and graduate faculty member in the Department of Geological Sciences at the University of Colorado. He was an Associate Curator in the Department of Paleontology and the Associate Director of the Department of PaleoServices at the San Diego Natural History Museum. Dr. Murphey has been working as a consultant and Principal Investigator for paleontological resource impact mitigation projects throughout the United States for approximately 22 years. He was the Principal Paleontologist of the Paleontological Resources Program at SWCA Environmental Consultants for 11 years. In 2014, he joined Los Angeles–based Paleo Solutions as a partner and Vice President, forming Denver-based Rocky Mountain Paleo Solutions. Dr. Murphey is currently a research associate in the Department of Earth Sciences at the Denver Museum of Nature and Science and the Department of Paleontology at the San Diego Natural History Museum. His research is focused on the evolutionary history, stratigraphy, biochronology, and depositional environments of Paleogene fossil mammals and associated rock units in the Rocky Mountain region and southern California.

Thomas Kelly received his B.A. and M.S. degrees in Biology from the California State University at Northridge (1968 and 1969) and a doctorate in Veterinary Medicine (DVM) from the University of California at Davis (1973). He did postgraduate research concentrating on the phylogenetic systematics of heteromyid rodents at the University of California, Davis in 1973-74. Since 1988, he has been a Research Associate in the Vertebrate Paleontology Department at the Natural History Museum of Los Angeles County and has been working as a consultant for paleontological resource impact mitigation projects in California for the last 25 years. He has published 52 paleontological articles, 39 of which were in peer-reviewed scientific journals. He has been the author or co-author of a number of new taxa in the paleontological literature, including nine mammal genera, 33 mammal species and one fish species. His interests are primarily in mammalian systematics and biostratigraphy.